The ACIAR-managed project CS1/1996/013, Herbicide-resistant weeds of wheat in India and Australia: integrated management, was designed to find a long-term method of control of Phalaris minor, a problem weed of the rice–wheat cropping system of north-western India. By 1993, the weed had developed resistance to isoproturon, a herbicide which had delivered effective weed control for 15 years. The short-term solution, implemented before the ACIAR project commenced, involved identification and registration of a new set of herbicides. But these new herbicides were expensive. To ensure high adoption they needed to be combined with changes in wheat-growing techniques that would provide cost savings to help farmers pay for them. And to avoid the re-emergence of chemical resistance, they needed to be used sparingly as one element in a broader approach to weed management. The project team used these circumstances to field-test and encourage adoption of zero tillage, a technology that agronomists had been advocating for many years, but which had failed to capture the interest of Indian farmers. Zero tillage has the potential to deliver big cost savings. In addition, it provides prospects for yield increases by allowing early sowing of wheat and avoiding soil degradation. Project research established that zero tillage also provided effective weed control with only a moderate reliance on chemicals, making the re-emergence of herbicide resistance remote. We calculate a gain to the Indian economy of around $1800 million in net present value terms over the next 30 years from the adoption of zero tillage to control Phalaris minor infestation in the rice–wheat areas of north-western India. This leads to an extremely high ratio of benefits to project costs. Zero tillage by itself is clearly a profitable technology. It does not need a weed problem to justify its introduction. Without the ACIAR project, zero tillage would have been introduced to the region, though somewhat later than what has occurred. On the assumption that the ACIAR project has advanced the adoption profile of zero tillage by 3 years, we calculate gains that can be attributed to ACIAR’s role of $238 million in net present value terms over the next 30 years. This gain has been achieved with total expenditures on the ACIAR-managed project amounting to only $1.3 million in present values.